Pumping stations or tanks that contain hazardous and/or flammable or volatile liquids and chemicals to be pumped at predetermined levels are capable of containing gases that could explode if an electrical arc becomes present. Float switches are commonly used in this application to detect level for activation of a pump (see FIG. 2), but must have electrical current that passes through wires and a switch housed within the float. Wires from the float switch run to a control panel located external to the tank or pit and is located outside the hazardous area. As liquids rises in the tank the float tilts and a ball or conductive liquid, such as mercury, moves and makes contact with an electrical switch or contacts of some sort causing the switch to activate. Electrical current then passes from the control panel through the wires, to the switch, completing the circuit. These all cause a spark within the float that could cause an explosion if the float malfunctions. The wires leading to the float are also a source of arcing which can occur if the wires are damaged.
Some tanks containing flammable liquids or gases use ultra sonic level detection which sends a sonic burst to the surface of the liquid and then back. The transit time of the beam is used to determine the liquid level. No electrical current is used within the tank or pit and the transmitter and receiver are located external to the hazardous atmosphere. This method is not generally used to remotely signal a device, such as a signal to engage/disengage a pump (such as a dosing pump) at discrete levels, as these level detectors will detect all heights and hence additional logic circuits are needed to select a predetermined height for operation of a pump, thereby raising the complexity and expense of such as system.